310 syringe problems

Hi 310 users
Our latest problem with the 310 is that of the syringe moving down 3-7x
more than usual. We get nice runs with sharp peaks in the correct place but
run out of polymer at a horrendous rate. The syringe has been calibrated,
butthe problem is not getting better, in fact it's getting worse. Has
anyone else had a similar problem, and what's the solution?
Thanks
Agnes